A new scheme for rapid epitope mapping of the recognition sequence of antigens, receptor lingands, etc. has been devised, involving four steps. Step 1. Rapid digestion of a protein with one or several proteases. Step 2. Immunoprecipitation of the fragments with, for example, a monoclonal antibody, receptor, etc. against the protein antigen. Step 3. Matrix-assisted laser desorption mass spectrometric determination of the peptide(s) that associate with the antibody, receptor, etc. Step 4. Determination of the precise linear epitope with synthetic peptide ladders. Affinity mass spectrometry was used to determine epitopes for Anti-melittin, anti-GLP-17-37 and anti-hbFGF monoclonal antibodies. A paper describing the technique was submitted for publication in PNAS.rough repetitive amino acid residues. We are using mass spectrometrein inhibiting ocidoreductase activity. Recombinant dsbA protein and SeMet dsbA was overexposed in E-coli to determine the protein sturcutre by x-ray crystallography. We would like to know the molecular mass of dsbA and SeMet dsbA to determine how well the methionine has been replaced by Se methionine.